September 30, 2010

It’s almost time to call metamaterials simply that science fiction stuff. Usually you hear about metamaterials around these parts in posts about actual invisibility cloaking technology, and here’s one about metamaterials and warp drives. Metamaterials — turning science fiction into science fact …

From the link:

That means physicists can use metamaterials to simulate the universe itself and all the weird phenomenon of general relativity. We’ve looked at various attempts to recreate black holes, the Big Bang and even multiverses.

But there’s another thing that general relativity appears to allow: faster than light travel. In 1994, the Mexican physicist, Michael Alcubierre, realised that while relativity prevents faster-than-light travel relative to the fabric of spacetime, it places no restriction on the speed at which regions of spacetime can move relative to each other.

That suggests a way of building a warp drive. Alcubierre imagined a small volume of flat spacetime in which a spacecraft sits, surrounded by a bubble of spacetime that shrinks in the direction of travel, bringing your destination nearer, and stretches behind you. He showed that this shrinking and stretching could enable the bubble–and the spaceship it contained–to move at superluminal speeds.

Today, Igor Smolyaninov at the University of Maryland, points out that if these kinds of bubbles are possible in spacetime, then it ought to be possible to simulate them inside a metamaterial.

New findings promising for ‘transformation optics,’ cloaking

WEST LAFAYETTE, Ind. — Researchers have overcome a fundamental obstacle in using new “metamaterials” for radical advances in optical technologies, including ultra-powerful microscopes and computers and a possible invisibility cloak.

The metamaterials have been plagued by a major limitation: too much light is “lost,” or absorbed by metals such as silver and gold contained in the metamaterials, making them impractical for optical devices.

However, a Purdue University team has solved this hurdle, culminating three years of research based at the Birck Nanotechnology Center at the university’s Discovery Park.

“This finding is fundamental to the whole field of metamaterials,” said Vladimir M. Shalaev, Purdue’s Robert and Anne Burnett Professor of Electrical and Computer Engineering. “We showed that, in principle, it’s feasible to conquer losses and develop these materials for many applications.”

Research findings are detailed in a paper appearing on Aug. 5 in the journal Nature.

The material developed by Purdue researchers is made of a fishnet-like film containing holes about 100 nanometers in diameter and repeating layers of silver and aluminum oxide. The researchers etched away a portion of the aluminum oxide between silver layers and replaced it with a “gain medium” formed by a colored dye that can amplify light.

Other researchers have applied various gain media to the top of the fishnet film, but that approach does not produce sufficient amplification to overcome losses, Shalaev said.

Instead, the Purdue team found a way to place the dye between the two fishnet layers of silver, where the “local field” of light is far stronger than on the surface of the film, causing the gain medium to work 50 times more efficiently.

The approach was first developed by former Purdue doctoral student Hsiao-Kuan Yuan, now at Intel Corp., and it was further developed and applied by doctoral student Shumin Xiao.

Unlike natural materials, metamaterials are able to reduce the “index of refraction” to less than one or less than zero. Refraction occurs as electromagnetic waves, including light, bend when passing from one material into another. It causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside.

Being able to create materials with an index of refraction that’s negative or between one and zero promises a range of potential breakthroughs in a new field called transformation optics. Possible applications include a “planar hyperlens” that could make optical microscopes 10 times more powerful and able to see objects as small as DNA; advanced sensors; new types of “light concentrators” for more efficient solar collectors; computers and consumer electronics that use light instead of electronic signals to process information; and a cloak of invisibility.

Excitement about metamaterials has been tempered by the fact that too much light is absorbed by the materials. However, the new approach can dramatically reduce the “absorption coefficient,” or how much light and energy is lost, and might amplify the incident light so that the metamaterial becomes “active,” Shalaev said.

“What’s really important is that the absorption coefficient can be as small as only one-millionth of what it was before using our approach,” Shalaev said. “We can even have amplification of light instead of its absorption. Here, for the first time, we showed that metamaterials can have a negative refractive index and amplify light.”

First, the researchers had to learn how to precisely remove as much as possible of the aluminum oxide layer in order to vacate space for dye without causing a collapse of the structure.

“You remove it almost completely but leave a little bit to act as pillars to support the structure, and then you spin coat the dye-doped polymer inside the structure,” he said.

The researchers also had to devise a way to deposit just the right amount of dye mixed with an epoxy between the silver layers of the perforated film.

“You can’t deposit too much dye and epoxy, which have a positive refractive index, but only a thin layer about 50 nanometers thick, or you lose the negative refraction,” Shalaev said.

Future work may involve creating a technology that uses an electrical source instead of a light source, like semiconductor lasers now in use, which would make them more practical for computer and electronics applications.

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The work was funded by the U.S. Army Research Office and the National Science Foundation.

Hit this link for the related image (it’s just too big for this blog and I didn’t feel like doing any resizing), and here’s the accompanying caption for the image:

This illustration shows the structure of a new device created by Purdue researchers to overcome a fundamental obstacle in using new “metamaterials” for radical advances in optical technologies, including ultrapowerful microscopes and computers and a possible invisibility cloak. The material developed by the researchers is a perforated, fishnet-like film made of repeating layers of silver and aluminum oxide. The researchers etched away a portion of the aluminum oxide between silver layers and replaced it with a “gain medium” to amplify light. (Birck Nanotechnology Center, Purdue University)

Uniquely versatile material could be used for more efficient light collection in solar cells

IMAGE: Arrays of coupled plasmonic coaxial waveguides offer a new approach by which to realize negative-index metamaterials that are remarkably insensitive to angle of incidence and polarization in the visible range….

PASADENA, Calif.—A group of scientists led by researchers from the California Institute of Technology (Caltech) has engineered a type of artificial optical material—a metamaterial—with a particular three-dimensional structure such that light exhibits a negative index of refraction upon entering the material. In other words, this material bends light in the “wrong” direction from what normally would be expected, irrespective of the angle of the approaching light.

This new type of negative-index metamaterial (NIM), described in an advance online publication in the journal Nature Materials, is simpler than previous NIMs—requiring only a single functional layer—and yet more versatile, in that it can handle light with any polarization over a broad range of incident angles. And it can do all of this in the blue part of the visible spectrum, making it “the first negative index metamaterial to operate at visible frequencies,” says graduate student Stanley Burgos, a researcher at the Light-Material Interactions in Energy Conversion Energy Frontier Research Center at Caltech and the paper’s first author.

“By engineering a metamaterial with such properties, we are opening the door to such unusual—but potentially useful—phenomena as superlensing (high-resolution imaging past the diffraction limit), invisibility cloaking, and the synthesis of materials index-matched to air, for potential enhancement of light collection in solar cells,” says Harry Atwater, Howard Hughes Professor and professor of applied physics and materials science, director of Caltech’s Resnick Institute, founding member of the Kavli Nanoscience Institute, and leader of the research team

What makes this NIM unique, says Burgos, is its engineering. “The source of the negative-index response is fundamentally different from that of previous NIM designs,” he explains. Those previous efforts used multiple layers of “resonant elements” to refract the light in this unusual way, while this version is composed of a single layer of silver permeated with “coupled plasmonic waveguide elements.”

Surface plasmons are light waves coupled to waves of electrons at the interface between a metal and a dielectric (a non-conducting material like air). Plasmonic waveguide elements route these coupled waves through the material. Not only is this material more feasible to fabricate than those previously used, Burgos says, it also allows for simple “tuning” of the negative-index response; by changing the materials used, or the geometry of the waveguide, the NIM can be tuned to respond to a different wavelength of light coming from nearly any angle with any polarization. “By carefully engineering the coupling between such waveguide elements, it was possible to develop a material with a nearly isotopic refractive index tuned to operate at visible frequencies.”

This sort of functional flexibility is critical if the material is to be used in a wide variety of ways, says Atwater. “For practical applications, it is very important for a material’s response to be insensitive to both incidence angle and polarization,” he says. “Take eyeglasses, for example. In order for them to properly focus light reflected off an object on the back of your eye, they must be able to accept and focus light coming from a broad range of angles, independent of polarization. Said another way, their response must be nearly isotropic. Our metamaterial has the same capabilities in terms of its response to incident light.”

This means the new metamaterial is particularly well suited to use in solar cells, Atwater adds. “The fact that our NIM design is tunable means we could potentially tune its index response to better match the solar spectrum, allowing for the development of broadband wide-angle metamaterials that could enhance light collection in solar cells,” he explains. “And the fact that the metamaterial has a wide-angle response is important because it means that it can ‘accept’ light from a broad range of angles. In the case of solar cells, this means more light collection and less reflected or ‘wasted’ light.”

“This work stands out because, through careful engineering, greater simplicity has been achieved,” says Ares Rosakis, chair of the Division of Engineering and Applied Science at Caltech and Theodore von Kármán Professor of Aeronautics and Mechanical Engineering.

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In addition to Burgos and Atwater, the other authors on the Nature Materials paper, “A single-layer wide-angle negative index metamaterial at visible frequencies,” are Rene de Waele and Albert Polman from the Foundation for Fundamental Research on Matter Institute for Atomic and Molecular Physics in Amsterdam. Their work was supported by the Energy Frontier Research Centers program of the Office of Science of the Department of Energy, the National Science Foundation, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek, and “NanoNed,” a nanotechnology program funded by the Dutch Ministry of Economic Affairs.

Since then, Baile Zhang and buddies at the Massachusetts Institute of Technology in Cambridge, have been busy looking for the weak point in this idea and now think they’ve found it. Today, they point out that carpet cloaks have a flaw that makes the objects within them detectable.

The problem, they say, is that isotropic cloaks cannot work perfectly. Here’s why. Light can be thought of as a series of wavefronts each with a certain amount of energy. Ordinarily, the direction of energy propagation is at right angles to these wavefronts.

However, in an invisibility cloak, this perpendicular relationship becomes distorted as the light waves are steered. That’s what an anisotropic material does. But an isotropic material cannot do this–the energy always propagates at right angles to the wavefronts. This limitation means that isotropic materials cannot hide objects in the way Pendry suggests.

Zhang and co go on to prove their assertion by tracing a ray that passes through the kind of isotropic carpet cloak that Pendry suggested. What they’ve discovered will shock carpet cloakers all over the world.

According to Zhang and buddies, carpet cloaks don’t hide objects, they merely shift them to one side by an amount that is just a bit less than they are high. Crucially the effect depends on the angle at which you are looking. So when illuminated at an angle of 45 degrees, an object 0.2 units tall appears laterally shifted by 0.15 units.

If Zhang and co are correct, this could be a substantial blow for isotropic carpet cloaking. It means that the carpet cloaking effect has a limited angle of view.

In a twist on the concept of an invisibility cloak, researchers have designed a material that not only makes an object invisible, but also generates one or more virtual images in its place. Because it doesn’t simply display the background environment to a viewer, this kind of optical device could have applications that go beyond a normal invisibility cloak. Plus, unlike previously proposed illusion devices, the design proposed here could be realized with artificial metamaterials.

The team of engineers, Wei Xiang Jiang, Hui Feng Ma, Qiang Cheng, and Tie Jun Cui from Southeast University in Nanjing, China, describes the recently developed class of optical transformation media as “illusion media.” As they explain in a new study, any object enclosed by such an illusion medium layer appears to be one or more other objects. The researchers’ proposed device is designed to operate at microwave frequencies.

“The illusion media make an enclosed object appear like another object or multiple virtual objects,” Cui told PhysOrg.com. “Hence it can be applied to confuse the detectors or the viewers, and the detectors or the viewers can’t perceive the real object. As a result, the enclosed object will be protected.”

Illusion media can transform a real image into a virtual image. For example, a golden apple (the actual object) enclosed within the illusion medium layer appears as two green apples (the illusion) to any viewer outside the virtual boundary (dashed curves). Image credit: Jiang, et al.

Researchers at Germany’s Karlsruhe Institute of Technology report they were able to cloak a tiny bump in a layer of gold, preventing its detection at nearly visible infrared frequencies.

Their cloaking device also worked in three dimensions, while previously developed cloaks worked in two dimensions, lead researcher Tolga Ergin said.

The cloak is a structure of crystals with air spaces in between, sort of like a woodpile, that bends light, hiding the bump in the gold later beneath, the researchers reported in Thursday’s online edition of the journal Science.

In this case, the bump was tiny, a mere 0.00004 inch high and 0.0005 inch across (100 microns x 30 microns), so that a magnifying lens was needed to see it.

“In principle, the cloak design is completely scalable; there is no limit to it,” Ergin said. But, he added, developing a cloak to hide something takes a long time, “so cloaking larger items with that technology is not really feasible.”

“Other fabrication techniques, though, might lead to larger cloaks,” he added in an interview via e-mail.

Active cloaking devices can use destructive interference, similar to noise-cancelling headphones, to render invisible areas up to 10 times larger than the wavelength of light being disguised and over large regions of space, University of Utah researchers have found.

The researchers predict that engineers will be able to use their method to create active invisibility cloaks that could shield submarines from sonar, planes from radar, and buildings from earthquakes.

A lot of this stuff is really getting deeper and deeper into the world of science fiction as science fact. Of course, I’m still waiting to see a convincing real-world demonstration of the basic cloaking technology touted the last few years, so maybe all this news remains in the world of fiction. Either way, it’s a fun topic.

Beyond the looking glass…

PhysOrg.com, Aug. 13, 2009

A “hidden portal” invisibility cloak may be possible using exotic new single-crystal yttrium-iron-garnet ferrite metamaterials that force light and other forms of electromagnetic radiation in complicated directions, researchers from the Hong Kong University of Science and Technologyand Fudan University have found.

July 7, 2009

Via KurzweilAI.net — I’ve done plenty of blogging on invisibility cloaking technology, and here’s the lastest. I think this tech is very cool and I hate to throw any cold water on the latest news, but I’d be more impressed with seeing an actual effective working model of a simple cloaking device before getting to wild with advanced varients like those described below.

Modified invisibility cloak could make the ultimate illusion

New Scientist Tech, July 7, 2009

An illusion device using metamaterials that makes one object look like another could one day be used to camouflage military planes or create “holes” in solid walls.

To make a cup look like a spoon, for example, light first strikes the cup and is distorted. It then passes through a complementary metamaterial which cancels out the distortions to make the cup seem invisible. The light then moves into a region of the metamaterial that creates a distortion as if a spoon were present. The result is that an observer looking at the cup through the metamaterial would see a spoon.

I’ve done plenty of blogging on invisibility cloaking technology. Here’s a release from yesterday on the very latest news. It does seem we’re getting pretty close to an actual invisibility cloak. Science fiction becomes science fact once again.

WEST LAFAYETTE, Ind. – Researchers have created a new type of invisibility cloak that is simpler than previous designs and works for all colors of the visible spectrum, making it possible to cloak larger objects than before and possibly leading to practical applications in “transformation optics.”

Whereas previous cloaking designs have used exotic “metamaterials,” which require complex nanofabrication, the new design is a far simpler device based on a “tapered optical waveguide,” said Vladimir Shalaev, Purdue University’s Robert and Anne Burnett Professor of Electrical and Computer Engineering.

Waveguides represent established technology – including fiber optics – used in communications and other commercial applications.

The research team used their specially tapered waveguide to cloak an area 100 times larger than the wavelengths of light shined by a laser into the device, an unprecedented achievement. Previous experiments with metamaterials have been limited to cloaking regions only a few times larger than the wavelengths of visible light.

Because the new method enabled the researchers to dramatically increase the cloaked area, the technology offers hope of cloaking larger objects, Shalaev said.

Findings are detailed in a research paper appearing May 29 in the journal Physical Review Letters. The paper was written by Igor I. Smolyaninov, a principal electronic engineer at BAE Systems in Washington, D.C.; Vera N. Smolyaninova, an assistant professor of physics at Towson University in Maryland; Alexander Kildishev, a principal research scientist at Purdue’s Birck Nanotechnology Center; and Shalaev.

“All previous attempts at optical cloaking have involved very complicated nanofabrication of metamaterials containing many elements, which makes it very difficult to cloak large objects,” Shalaev said. “Here, we showed that if a waveguide is tapered properly it acts like a sophisticated nanostructured material.”

The waveguide is inherently broadband, meaning it could be used to cloak the full range of the visible light spectrum. Unlike metamaterials, which contain many light-absorbing metal components, only a small portion of the new design contains metal.

Theoretical work for the design was led by Purdue, with BAE Systems leading work to fabricate the device, which is formed by two gold-coated surfaces, one a curved lens and the other a flat sheet. The researchers cloaked an object about 50 microns in diameter, or roughly the width of a human hair, in the center of the waveguide.

“Instead of being reflected as normally would happen, the light flows around the object and shows up on the other side, like water flowing around a stone,” Shalaev said.

The research falls within a new field called transformation optics, which may usher in a host of radical advances, including cloaking; powerful “hyperlenses” resulting in microscopes 10 times more powerful than today’s and able to see objects as small as DNA; computers and consumer electronics that use light instead of electronic signals to process information; advanced sensors; and more efficient solar collectors.

Unlike natural materials, metamaterials are able to reduce the “index of refraction” to less than one or less than zero. Refraction occurs as electromagnetic waves, including light, bend when passing from one material into another. It causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside. Each material has its own refraction index, which describes how much light will bend in that particular material and defines how much the speed of light slows down while passing through a material.

Natural materials typically have refractive indices greater than one. Metamaterials, however, can be designed to make the index of refraction vary from zero to one, which is needed for cloaking.

The precisely tapered shape of the new waveguide alters the refractive index in the same way as metamaterials, gradually increasing the index from zero to 1 along the curved surface of the lens, Shalaev said.

Previous cloaking devices have been able to cloak only a single frequency of light, meaning many nested devices would be needed to render an object invisible.

Kildishev reasoned that the same nesting effect might be mimicked with the waveguide design. Subsequent experiments and theoretical modeling proved the concept correct.

Researchers do not know of any fundamental limit to the size of objects that could be cloaked, but additional work will be needed to further develop the technique.

Recent cloaking findings reported by researchers at other institutions have concentrated on a technique that camouflages features against a background. This work, which uses metamaterials, is akin to rendering bumps on a carpet invisible by allowing them to blend in with the carpet, whereas the Purdue-based work concentrates on enabling light to flow around an object.

This image shows the design of a new type of invisibility cloak that is simpler than previous designs and works for all colors of the visible spectrum, making it possible to cloak larger objects than before and possibly leading to practical applications in “transformation optics.” (Purdue University)

Yep, news on invisibility cloaks returns once again. This time with a twist — metamaterials that can go beyond a simple cloak of invisibility and actually create the illusion of a totally different object in place of the one being cloaked.

Metamaterials could be used for an even more exotic effect than invisibility cloaks: to create the illusion that a different objectis present, Hong Kong University of Science and Technologyresearchers say.

A paper published in the March 2009 issue of SIAM Review, “Cloaking Devices, Electromagnetic Wormholes, and Transformation Optics,” presents an overview of the theoretical developments in cloaking from a mathematical perspective.

One method involves light waves bending around a region or object and emerging on the other side as if the waves had passed through empty space, creating an “invisible” region which is cloaked. For this to happen, however, the object or region has to be concealed using a cloaking device, which must be undetectable to electromagnetic waves. Manmade devices called metamaterials use structures having cellular architectures designed to create combinations of material parameters not available in nature.

Mathematics is essential in designing the parameters needed to create metamaterials and to show that the material ensures invisibility. The mathematics comes primarily from the field of partial differential equations, in particular from the study of equations for electromagnetic waves described by the Scottish mathematician and physicist James Maxwell in the 1860s.

One of the “wrinkles” in the mathematical model of cloaking is that the transformations that define the required material parameters have singularities, that is, points at which the transformations fail to exist or fail to have properties such as smoothness or boundness that are required to demonstrate cloaking. However, the singularities are removable; that is, the transformations can be redefined over the singularities to obtain the desired results.

Next generation cloaking device demonstrated

DURHAM, N.C. – A device that can bestow invisibility to an object by “cloaking” it from visual light is closer to reality. After being the first to demonstrate the feasibility of such a device by constructing a prototype in 2006, a team of Duke University engineers has produced a new type of cloaking device, which is significantly more sophisticated at cloaking in a broad range of frequencies.

The latest advance was made possible by the development of a new series of complex mathematical commands, known as algorithms, to guide the design and fabrication of exotic composite materials known as metamaterials. These materials can be engineered to have properties not easily found in natural materials, and can be used to form a variety of “cloaking” structures. These structures can guide electromagnetic waves around an object, only to have them emerge on the other side as if they had passed through an empty volume of space.

The results of the latest Duke experiments were published Jan. 16 in the journal Science. First authors of the paper were Duke’s Ruopeng Liu, who developed the algorithm, and Chunlin Li. David R. Smith, William Bevan Professor of electrical and computer engineering at Duke, is the senior member of the research team.

Once the algorithm was developed, the latest cloaking device was completed from conception to fabrication in nine days, compared to the four months required to create the original, and more rudimentary, device. This powerful new algorithm will make it possible to custom-design unique metamaterials with specific cloaking characteristics, the researchers said.

“The difference between the original device and the latest model is like night and day,” Smith said. “The new device can cloak a much wider spectrum of waves — nearly limitless — and will scale far more easily to infrared and visible light. The approach we used should help us expand and improve our abilities to cloak different types of waves.”

Cloaking devices bend electromagnetic waves, such as light, in such a way that it appears as if the cloaked object is not there. In the latest laboratory experiments, a beam of microwaves aimed through the cloaking device at a “bump” on a flat mirror surface bounced off the surface at the same angle as if the bump were not present. Additionally, the device prevented the formation of scattered beams that would normally be expected from such a perturbation.

The underlying cloaking phenomenon is similar to the mirages seen ahead at a distance on a road on a hot day.

“You see what looks like water hovering over the road, but it is in reality a reflection from the sky,” Smith explained. “In that example, the mirage you see is cloaking the road below. In effect, we are creating an engineered mirage with this latest cloak design.”

Smith believes that cloaks should find numerous applications as the technology is perfected. By eliminating the effects of obstructions, cloaking devices could improve wireless communications, or acoustic cloaks could serve as protective shields, preventing the penetration of vibrations, sound or seismic waves.

“The ability of the cloak to hide the bump is compelling, and offers a path towards the realization of forms of cloaking abilities approaching the optical,” Liu said. “Though the designs of such metamaterials are extremely complex, especially when traditional approaches are used, we believe that we now have a way to rapidly and efficiently produce such materials.”

With appropriately fine-tuned metamaterials, electromagnetic radiation at frequencies ranging from visible light to radio could be redirected at will for virtually any application, Smith said. This approach could also lead to the development of metamaterials that focus light to provide more powerful lenses.

The newest cloak, which measures 20 inches by 4 inches and less than an inch high, is actually made up of more than 10,000 individual pieces arranged in parallel rows. Of those pieces, more than 6,000 are unique. Each piece is made of the same fiberglass material used in circuit boards and etched with copper.

The algorithm determined the shape and placement of each piece. Without the algorithm, properly designing and aligning the pieces would have been extremely difficult, Smith said.

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The research was supported by Raytheon Missile Systems, the Air Force Office of Scientific Research, InnovateHan Technology, the National Science Foundation of China, the National Basic Research Program of China, and National Science Foundation of Jiangsu Province, China.

Others members of the research team were Duke’s Jack Mock, as well as Jessie Y. Chin and Tie Jun Cui from Southeast University, Nanjing, China.

An even greater problem for anyone who has aspirations to be concealed in public one day is that invisibility achieved through transformation media is a two-way street. With no light penetrating a perfect invisibility cloak, there would be no way for an invisible person to see outside. In other words, invisible people would also be blind—not exactly what Harry Potter had in mind.

But now, Chen and his colleagues have developed way to partially cancel the invisibility cloak’s cloaking effect. Their “anti-cloak” would be a material with optical properties perfectly matched to those of an invisibility cloak. (In technical jargon, an anti-cloak would be anisotropic negative refractive index material that is impedance matched to the positive refractive index of the invisibility cloak).

While an invisibility cloak would bend light around an object, any region that came into contact with the anti-cloak would guide some light back so that it became visible. This would allow an invisible observer to see the outside by pressing a layer of anti-cloak material in contact with an invisibility cloak

From KurzweilAI.net — I’ve blogged on 3D cloaking devices before, very likely the previous KurzweilAI.net linked blog post from mid-May is an earlier report of this project. Both stories originate from UC Berkeley.

PhysOrg.com, Aug. 10, 2008University of California, Berkeley scientists have created a multilayered, “fishnet” metamaterial that unambiguously exhibits negative refractive index, allowing for invisibility in three dimensions for the first time, Nature magazine plans to report this week.

Two breakthroughs in the development of metamaterials – composite materials with extraordinary capabilities to bend electromagnetic waves – are reported separately this week in the Aug. 13 advanced online issue of Nature, and in the Aug. 15 issue of Science.

Applications for a metamaterial entail altering how light normally behaves. In the case of invisibility cloaks or shields, the material would need to curve light waves completely around the object like a river flowing around a rock. For optical microscopes to discern individual, living viruses or DNA molecules, the resolution of the microscope must be smaller than the wavelength of light.

The common thread in such metamaterials is negative refraction. In contrast, all materials found in nature have a positive refractive index, a measure of how much electromagnetic waves are bent when moving from one medium to another.

In a classic illustration of how refraction works, the submerged part of a pole inserted into water will appear as if it is bent up towards the water’s surface. If water exhibited negative refraction, the submerged portion of the pole would instead appear to jut out from the water’s surface. Or, to give another example, a fish swimming underwater would instead appear to be moving in the air above the water’s surface

And here’s the image:

On the left is a schematic of the first 3-D “fishnet” metamaterial that can achieve a negative index of refraction at optical frequencies. On the right is a scanning electron microscope image of the fabricated structure, developed by UC Berkeley researchers. The alternating layers form small circuits that can bend light backwards. Image by Jason Valentine, UC Berkeley

A researcher at the University of California at Berkeley claims to have made a 3D metamaterial with a negative refractive index, the first 3D material of this kind.

Physicists have in recent years made it possible to bend, or refract, light in the opposite direction to any natural materials. These metamaterials make it possible to create invisibility cloaks that hide an object by steering light around it. The materials and “invisibility cloaks” built so far have all been flat, working only in two dimensions.

The negative refraction index will have to be confirmed by measuring the speed of light in the material.